Photographic element comprising an opaque backcoat

ABSTRACT

A backing or antihalation layer for a photosensitive element containing carbon black additionally contains a salt of a heavy metal. The heavy metal inhibits fog formation in the silver halide emulsion of the photosensitive element.

finite tates atent [1 1 MacLeish et a1.

[ Aug. 19, 1975 PHOTOGRAPHIC ELEMENT COMPRISING AN OPAQUE BACKCOATInventors: William T. MacLeish, North Andover; Terry W. Milligan,Belmont, both of Mass.

Assignee: Polaroid Corporation, Cambridge,

Mass.

Filed: Oct. 23, 1973 Appl, No.: 408,374

US. Cl. 96/84 R; 96/84 M; 96/87 R;

96/110; 252/300 Int. C13. G03C 1/84 Field of Search 96/84 M, 87 A, 84 RReferences Cited UNITED STATES PATENTS 11/1922 Seel 96/87 A PrimaryExaminer-Ronald H. Smith Attorney, Agent, or FirmPhilip G. Kiely 5 7ABSTRACT A backing or antihalation layer for a photosensitive elementcontaining carbon black additionally contains a salt of a heavy metal.The heavy metal inhibits fog formation in the silver halide emulsion ofthe photosensitive element.

7 Claims, No Drawings PHOTOGRAPI-IIC ELEMENT COMPRISING AN OPAQUEBACKCOAT BACKGROUND OF THE INVENTION Photosensitive elements often havelight-absorbing layers coated on one side of the silver halide emulsionlayer to avoid exposure of an underlying film unit, or as anantihalation layer. For convenience, the lightabsorbing layers will bereferred to as backing layers. These backing layers may be applieddirectly to one side of the emulsion or on the reverse side of a supportwhich carries the emulsion. Even though a support separates the emulsionfrom the backing layer, there can still be contact because in a roll offilm some portion of the emulsion will contact the backing. With stackedfilm units, there is usually front-to-back contact.

The backing layers may be opaque or only sufficiently light-absorbing asto prevent the above-mentioned exposure of the emulsion layer orunderlying film units or, as in the case of antihalation layers,sufficiently light absorptive to avoid undesirable reflections from thefilm base or from interfaces between the emulsion layer and otherlayers, which, if not avoided, cause additional diffused exposure of thesilver halide emulsions.

The above-described light-absorbing qualities of the backing layer maybe provided by dyes, pigments or silver. Silver is relatively expensivebecause of the amount necessary and usually two or three dyes arerequired in backing layers to provide the desired degree of lightabsorption.

One of the most commonly used and effective lightabsorbing materials iscarbon black. However, it is well known that the presence of carbonblack in a layer of a film unit adversely effects the silver halideemulsion layer. Specifically, an appreciable fog level is noted, as afunction of time on stored film units employing carbon black as acomponent of the backing layer. Fading of the latent image has also beenreported as an effect attributable to the carbon black.

A novel backing layer has now been found which is not susceptible to thedeficiencies of the prior art.

SUMMARY OF THE INVENTION The present invention is directed to aphotosensitive element comprising at least one silver halide emulsionlayer and a backing layer containing carbon black and a salt of a heavymetal. Preferably, water-soluble salts are employed.

DETAILED DESCRIPTION OF THE INVENTION It has now been found thatwater-soluble heavy metal salts capable of forming relatively insolublesulfides disposed in carbon black-containing layers'of film unitsinhibit fog formation in the silver halide layer to a significantdegree. Specifically, water-soluble salts of silver, copper (cupric),platinum, palladium, zinc, cadmium, lead, iron (ferrous and ferric) andbismuth provide the above-described enhanced stability.

It has been found that the cation is the active species .in the presentinvention and, therefore, substantially any anion may be employed solong as it will not deleteriously react with other components of thecarbon black layer or interfere with the proper photographic employmentof the film unit.

Suitable anions include, but are not limited to, ni-

. trate, fluoride, sulfate, perrhenate, bromide, chloride 2 and acetate.The salt may be added to the carbon black mix prior to coating the layeror may be formed in situ.

While not intending to be bound by theory, it is believed that sulfur ora sulfur-containing compound is associated with the carbon black thatresults in the fogging of the silver halide during storage. The factthat the silver halide and the carbon black layer are not necessarily indirect, physical contact for fogging to occur indicates that the vaporphase may be involved. It is believed that the presence of the heavymetal salt reacts with the sulfur or sulfur-containing compound, formingan insoluble sulfide thereby rendering it unavailable for contaminationof the silver halide.

The concentration of the heavy metal salt varies with the particularsalt and with the particular type of carbon black employed.Unexpectedly, appreciable effects have been noted at relatively lowlevels. La, els ranging from 100 to 10,000 ppm (based on total solids ofcoating mix) and more have been employed.

It is also believed that it may not be necessary that the heavy metalsalt be distributed throughout the entire carbon black coating to beeffective. Surprisingly, a significant decrease in fog has been noted insilver halide emulsions in areas of the emulsions not in contact withthe compositions of the present invention but surrounding it.

The novel compositions of the present invention were evaluated in thefollowing manner.

The following master batch was prepared:

Elvanol -05 25 Elvanol T-25 Carbon black 50 g GAF S630" Voranol RN-485l. A fully hydrolyzed but water-soluble polyvinyl alcohol sold by E. I.DuPont de Nemours, Inc., Wilmington, Delaware.

2. A medium molecular weight, fully hydrolyzed polyvinyl alcohol sold byE. I. DuPont de Nemours, Inc., Wilmington, Delaware.

3. A polyvinylpyrrolidone/vinyl acetate copolymer sold by GAF Corp, NewYork, New York.

4. A polyether polyol sold by the Dow Chemical Company, Midland,Michigan.

A water solution of the polyvinyl alcohol and polyvinylpyrrolidone/vinylacetate copolymer was prepared to which the carbon black was added as anaqueous dispersion. Enough water was used to provide 14.0 percent totalsolids.

The various salts to be tested were prepared as 1.0 percent solutions inwater. In some cases, the mixture contained both dissolved andundissolved material but was treated as if it were all in solution whenaliquots are taken.

The carbon black mixes containing the salt additives were coated on anunsubbed polyester film base using a 6.0 mil fixed clearance bar. Thesecoatings were then dried for 3 minutes at 194 F. and then conditionedfor 24 hours at 75 F. and 45 percent R.H. before testing.

Pieces 2 X 3% inches were cut from the test coatings and interleaved infilm packs between a photographic emulsion coated on dye back base;i.e., base with only a dye antihalation layer on the back side and anopaque top layer. The test pieces were placed with the test back coat incontact with the emulsion. The test packs were sealed inpolyethylene/foil pouches and stored in an oven at 120 F. for 5 daysafter which they are allowed to equilibrate to room conditions. Thepacks are then processed as black spreads (unexposed) with freshprocessing composition and receiving sheets suitable for silverdiffusion transfer processing, and the antihalation layer was removedfrom the negatives. The negatives are then examined by transmitted lightfor evidence of chemical fog in the area in contact with the test backcoat and also in the surrounding area. Each sample was given a visualrating on a scale of to 10 with 0 indicating no fog and 10 indicatingcomplete fog. A control was designated as having a rating of 5.

The effects of the heavy metal salts are tabulated below.

4 backing for a receiving layer, mask, dark slide film package and thelike.

What is claimed is:

l. A photographic element which includes at least one silver halideemulsion layer and which also includes a layer containing carbon blackand a water-soluble salt of a heavy metal capable of forming arelatively insoluble sulfide.

2. A product as defined in claim 1 wherein said metal is selected fromthe group consisting of silver, copper, platinum, palladium, zinc,cadmium, lead, iron and bismuth.

3. A product as defined in claim 2 which includes a support carryingsaid carbon black layer on a first side TABLE 1 RELATIVE CONTAMINATIONRATING K of Cation Anion Formula Sul fide 100-" ppm 500 1,000 5,00010,000

SILVER Nitrate AgNO 10- 2 2 0 0 0 Fluoride AgF 0 0 Sulfate Ag SO 0 0Pcrrhenatc AgReO 0 0 COPPER Sulfate CuSO '5H O 6 2 l 0 O NitrateChloride PLATINUM Chloride K PtCh 1 0 PALLADIUM Chloride K- PdCh l 0ZINC Acetate Zn(OAc) '2H O 10- 5 5 5 2 0 CADMIUM Acetate Cd(OAc) -2H Ol0 5 5 3 2 2 LEAD Sub-Acetate 10- 4 4 4 3 2 BISMUTH Nitrate Bl No ,-si-:o 10- 2 IRON Chloride FcCl '4H O l0 0 Nitrate Fe(NO '9H O d 0 I listedin the literature as forming an insoluble sulfide, d listed in theliterature as forming a sulfide which decomposes in water.

From the foregoing it will be seen that the fog level of and said silverhalide emulsion layer on said second the negative was significantlyreduced from the control side. level of 5 and, in many instances,totally eliminated. 4. A product as defined in claim I wherein saidheavy As stated above, the novel compositions are particumetal salt issilver nitrate. larly useful as light-absorbing layers and antihalation5. A product as defined in claim 1 wherein said heavy layers. Forexample, the novel compositions are particmetal salt is present at alevel of at least 100 ppm based ularly useful as the removable backinglayer in the film 40 on the weight of said carbon black layer. unitsdisclosed and claimed in copending application 6. A product as definedin claim 1 wherein said car- Ser. No. 239,582, filed Mar. 20, 1972. bonblack layer includes a polymeric binder.

It should be understood, however, that the novel 7. A product as definedin claim 6 wherein said polycompositions are suitable for use wherever alightmeric binder includes polyvinyl alcohol. absorbing layer isdesired, for example, as an opaque

1. A PHOTOGRAPHIC ELEMENT WHICH INCLUDES AT LEAST ONE SILVER HALIDEEMULSION LAYER AND WHICH ALSO INCLUDES A LAYER CONTAINING CARBON BLACKAND A WATER-SOLUBLE SALT OF A HEAVY METAL CAPABLE OF FORMING ARELATIVELY INSOLUBLE SULFIDE.
 2. A product as defined in claim 1 whereinsaid metal is selected from the group consisting of silver, copper,platinum, palladium, zinc, cadmium, lead, iron and bismuth.
 3. A productas defined in claim 2 which includes a support carrying said carbonblack layer on a first side and said silver halide emulsion layer onsaid second side.
 4. A product as defined in claim 1 wherein said heavymetal salt is silver nitrate.
 5. A product as defined in claim 1 whereinsaid heavy metal salt is present at a level of at least 100 ppm based onthe weight of said carbon black layer.
 6. A product as defined in claim1 wherein said carbon black layer includes a polymeric binder.
 7. Aproduct as defined in claim 6 wherein said polymeric binder includespolyvinyl alcohol.